## The design for a simple portable computer that only requires a pen and a piece of paper.

The computer consists of a sheet of paper that contains both the program as well as a number of data registers, that will be used to represent the contents of the registers.

To begin, the pen, representing the program counter, is positioned at the line 00 of a program. The instruction in that line is then processed by the user by either moving the pen(program counter), modifying the value of a data register or by checking if a data register has become zeroed.

### Primitives

Most models contain a few arithmetic operations and at least one conditional operation. Three base models, each using three instructions, are drawn from the following collection. In addition, a machine usually has a HALT instruction, which stops the machine.

• CLR(r): CLeaR register r. (Set r to zero.)
• INC(r): INCrement the contents of register r.
• DEC(r): DECrement the contents of register r.
• CPY(rj, rk): CoPY the contents of register rj to register rk leaving the contents of rj intact.
• JZ(r, z): IF register r contains Zero THEN Jump to instruction z ELSE continue in sequence.
• JE(rj, rk, z): IF the contents of register rj Equals the contents of register rk THEN Jump to instruction z ELSE continue in sequence.

The following three counter machine models have the same computational power since the instructions of one model can be derived from those of another:

• INC(r), DEC(r), JZ(r, z) — Minsky (1961, 1967), Lambek (1961)
• CLR(r), INC(r), JE(rj, rk, z) — Ershov (1958), Peter (1958)
• INC(r), CPY(rj, rk), JE(rj, rk, z) — Elgot-Robinson (1964), Minsky (1967)

### WDR Instruction Set

The WDR paper computer or Know-how Computer is an educational model of a computer consisting only of a pen, a sheet of paper, and individual matches in the most simple case. The instruction set of five commands is small but Turing complete and therefore enough to represent all mathematical functions: incrementing ("inc") or decrementing ("dec") a register, unconditional jump ("jmp"), conditional jump ("skp", skips next instruction if a register is zero), and stopping program execution ("end").

OpcodeDescription
ENDAborts the execution of your program, so that you can examine the contents of your data registers.
SKP(r)Checks if the data register r is zero. If it is zero, the program counter is increased by 2, otherwise the program counter is increased only by 1.
JMP(z)Sets the program counter to line number z.
INC(r)Increments the contents of the data register r and increases the program counter by 1.
DEC(r)Decrements the contents of the data register r and increases the program counter by 1.

### Punched card

To encode a WDR program into a 8-bits punched card, we could use 3 bits of space to encode the operation, which leaves 5 bits for the value. This computer's programs uses only 5 operations out of a possible 8, leaving 3 unused.

BinaryOpcode
000END
001SKP
010JMP
100SUB

The following program subtracts from R1 and adds to R0 until the value of R1 is zero. The result of the addition of R0 and R1 will be stored in R0.

LineOpcodeValueOpcodeHex
0001000011JMP 03\$43
0210000001SUB R1\$82
0300100001SKP R1\$22
0401000001JMP 01\$41
0500000000END\$00

The binary expression of the operation and value of the previous program can be encoded horizontally as the following punched card:

v   v   v   v   v   v
•
•   •           •
•       •

•
•       •   •   •

### Ref. 5-bits Table

The following table show the binary table for 32 addressable lines of a program.

 00 00000 08 01000 10 100000 18 11000 01 00001 09 01001 11 100001 19 11001 02 00010 0A 01010 12 100010 1A 11010 03 00011 0B 01011 13 100011 1B 11011 04 00000 0C 01100 14 100000 1C 11100 05 00001 0D 01101 15 100001 1D 11101 06 00010 0E 01110 16 100010 1E 11110 07 00011 0F 01111 17 100011 1F 11111

### CARDIAC Instruction Set

CARDIAC (CARDboard Illustrative Aid to Computation) is a learning aid developed for Bell Telephone Laboratories in 1968 to teach high school students how computers work. The computer operates in base 10 and has 100 memory cells which can hold signed numbers from 0 to 999. It has an instruction set of 10 instructions which allows CARDIAC to add, subtract, test, shift, input, output and jump.

OpcodeInstructionDescription
INPInputtake a number from the input card and put it in a specified memory cell.
CLAClear and addclear the accumulator and add the contents of a memory cell to the accumulator.